Human GRK4 variants regulate renal angiotensin AT1 receptor expression

Abstract

Variants of the GRK4γ gene are associated with essential hypertension. Constitutively active GRK4 variants are linked with decreased function of the renal dopamine D1 receptor and increased expression of the angiotensin II type 1 receptor (AT1R). Renal AT1R mRNA and protein expressions are greater in transgenic mice expressing human (h) GRK4γ 142V variant than hGRK4γ wild-type (WT) (240±50 vs 100±15%, qRT-PCR, n=5, P<0.05, 150±8 vs 100±5 8%, western blot, n=5, P<0.05). Luciferase assays performed in human renal proximal tubule cells (hRPTC) co-transfected with the hAT1R promoter and hGRK4γ WT or hGRK4γ 142V showed that hGRK4γ WT decreases hAT1R promoter activity (60%, n=6, P<0.01) while hGRK4γ 142V increases it (400%, n=6, P<0.01). We hypothesized that GRK4 gene variants act in the nucleus to phosphorylate histone deacetylases (HDAC) and increase AT1R transcription. We found nuclear localization of GRK4 (laser confocal microscopy) and the presence of GRK4 and class I HDACs, HDAC1, HDAC2 and HDAC3, in purified nuclear extracts from hRPTCs. Nuclear GRK4 expression was greater in hRPTCs with GRK4 gene variants than those with WT GRK4. Co-immunoprecipitation experiments demonstrated physical interaction between GRK4 and HDAC1 and between GRK4 and HDAC2. Our results suggest that GRK4 may regulate AT1R expression by regulating HDAC activity.